Transparency in widgets does not work in UE 5.4.

In the widget editor, I set the Tint color for border alpha to 0.6 , for example. The transparency is Ok in the widget, but when I add the widget to the scene, the transparency is gone.
In version 5.1, transparency worked fine.
Does anyone know how to fix this, or should we wait for the developers to fix this bug?"

I have found the solution by myself !

You need to set Blend Mode → transporent in the Widget Component settings.